question_answer

A railway engine whistling at a constant frequency moves with a constant speed. It goes past a stationary observer beside the railway track.  Which of the following graphs best represent the variation of frequency of the sound n heard by the observer with the time t?

A)                                                                   

B)

C)                                                                  

D)

Correct Answer: B

Solution :

\[\upsilon =\]velocity of sound. \[{{f}_{1}}'=\frac{\upsilon }{\upsilon -u}f\] When source moves towards stationary observer. \[f'=\frac{\upsilon }{\upsilon +u}f\] When source moves away from observer. \[{{f}_{1}}'>f'\] \[f\]does not depend on time elapse (t).